Aerobic capacity in rate modulated pacing

Impact of rate-modulated pacing on quality of life and exercise capacity—Evidence from the Advanced Elements of Pacing Randomized Controlled Trial (ADEPT)

BACKGROUND

Ninety-nine percent of pacemakers implanted in the United States include an option for rate modulation.

OBJECTIVE

The purpose of this study was to determine whether dual-chamber rate-modulated pacing, when compared with dual-chamber pacing alone, improved quality of life.

METHODS

This was a single-blind randomized controlled trial comparing dual-chamber with rate-modulated dual-chamber pacing. Patients were enrolled between January 12, 2000, and January 10, 2002, with 1-year follow-up ending December 19, 2002. The study was a U.S. multicenter trial, with 95 sites participating. All patients received a rate modulation-capable dual-chamber pacemaker for standard indications. Patients were screened with an exercise test (Chronotropic Assessment Exercise Protocol) 1 month later. One thousand two hundred seventy-three patients were enrolled; 401 proved ineligible, and 872 (68%) made up the randomized patient cohort. Randomized patients had a mean age of 71 years, 64% were men, and 64% had sinus node dysfunction. Randomization was in a factorial design to (1) dual-chamber rate-modulated pacing versus dual-chamber pacing and (2) automatic mode switching versus no automatic mode switching. The present report is limited to the comparison of rate modulation with no rate modulation (DDDR vs. DDD). The primary endpoint was the score on the Specific Activity Scale, an activity-based cardiovascular disease-specific instrument at 1 year. Secondary endpoints included 6-month treadmill time and additional cardiovascular disease-specific, and generic health-related quality-of-life instruments at 1 year.

RESULTS

At 6 months, patients with rate modulation had a higher peak exercise heart rate (rate modulation 113.3 +/- 19.6, no rate modulation 101.1 +/- 21.1; P <.0001). Total exercise time was not different between groups. At 1 year, there were no significant differences between groups with respect to Specific Activity Scale or the secondary quality-of-life endpoints.

CONCLUSIONS

We conclude that rate modulation is ineffective in improving the functional status or quality of life of patients with a bradycardia indication for dual-chamber pacing.

Chronotropic Incompetence in Patients with an Implantable Cardioverter Defibrillator: Prevalence and Predicting Factors

Chronotropic incompetence (CI), which has not been systematically examined in the ICD patient population, may have implications for device programming. A total of 123 ICD patients were classified into three groups: single-chamber ICD with sinus rhythm, dual-chamber ICD with sinus rhythm, and single-chamber ICD with permanent atrial fibrillation. Heart rate response, maximum oxygen uptake, and oxygen uptake at the anaerobic threshold were measured during treadmill exercise testing. In addition, clinical variables such as antiarrhythmic drug therapy, underlying heart disease, and left-ventricular (LV) ejection fraction were recorded. Of the patients studied, 38% were chronotropically incompetent (47/123). Significant predictors of CI were as follows: presence of a coronary disease (P = 0.036), prior cardiac surgery (P = 0.037), chronic drug therapy with beta-blockers (P = 0.032), administration of amiodarone (P = 0.025), and a combination of these two forms of treatment (P = 0.01). Spiroergometry revealed reduced exercise capacity (P = 0.041) and lessened VO2max (P = 0.034) among chronotropically incompetent patients. A large percentage of ICD patients demonstrates CI with subsequently reduced physical stress tolerance. In light of the DAVID study, we believe that a closer examination of rate-adaptive modes for ICD patients is warranted under enhanced conditions: (1) optimized AV interval programming; (2) utilization of new algorithms to reduce ventricular pacing in combination with rate-adaptive atrial pacing, with the goal of addressing CI while minimizing ventricular pacing; and (3) an optimized upper heart-rate limit.

Hemodynamic sensors

Present adaptive-rate pacemakers use a range of sensors for implementation in open-loop and closed-loop control systems. Hemodynamic sensors that detect the mechanical action of the heart and blood flow offer additional features to implement physiologic rate adaption in rate-controlling systems and rate-limiting systems. Examples of 2 such sensors are presented.

Past and future technologic developments for rhythm and conduction disturbances

Since the first cardiac pacemaker was implanted in 1958, continuing technologic innovations have steadily improved the therapeutic power of implantable cardiac device therapy. This evolution has benefited both patients and their physicians, expanding the conditions manageable through pacing and implantable defibrillation while streamlining implant and follow-up procedures. This progress is likely to continue unabated because (1) devices will continue to grow smaller; (2) more advanced features will be introduced, with an increased level of automaticity; and (3) the quality and quantity of telemetered diagnostic information about both patient and device will continue to expand, and device sophistication will soon reach the point at which prediction and prevention of specific events will be a reality. This article reviews historical developments and presents concepts that are guiding future technologic innovations.

Influence of the pacing rate on the atrioventricular conduction time during aerobic and anaerobic exercise: basic concepts for a dromotropically controlled rate responsive pacemaker

The dromotropic pacemaker concept needs a rate responsive algorithm in which the pacing rate is controlled by the atrioventricular conduction time (AVCT). To develop basic concepts for such a rate responsive algorithm, the influence of the pacing rate on the AVCT was investigated. Seven patients (62 +/- 7.8 years) with sick sinus syndrome and intact atrioventricular conduction underwent two cardiopulmonary exercise tests (CPX) on a treadmill. According to the determination of the anaerobic threshold (AT) and the patients maximum capacity in the first incremental CPX the work rate for two exercise levels below and above the AT were chosen for the second constant workload CPX. The calculation of the optimal pacing rate (HRopt) was based on the oxygen uptake (VO2) during exercise after reaching steady-state conditions. According to the increase of the VO2 from 14.8 +/- 2.3 mL/min per kilogram during aerobic work (38.3 +/- 16.0 W) to 19.4 +/- 4.7 mL/min per kilogram during anaerobic work (80.6 +/- 32.3 W), the HRopt was calculated to be 98.6 +/- 6.9 beats/min and 116.4 +/- 4.7 beats/min. Starting from HRopt, the pacing rate was increased (overpacing) and decreased (underpacing) by about 5 beats/min every minute. At optimal pacing rate the AVCT decreased significantly from 233.0 +/- 30.5 ms during aerobic work and to 226.4 +/- 27.3 ms during anaerobic work (P < 0.05). Whereas overpacing induced a significant prolongation of the AVCT during aerobic work (4.17 +/- 1.78 ms per 10 beats/min) and anaerobic work (3.84 +/- 1.60 ms per 10 beats/min), underpacing yielded a significant shortening of the AVCT by about 4.49 +/- 2.64 ms per 10 beats/min during aerobic work and 4.75 +/- 1.87 ms per 10 beats/min during anaerobic work (P < 0.01). The slopes of the regression lines of the relationship between AVCT and pacing rate were not significantly. different. Based on the reciprocal relationship of heart rate (HR) and AVCT, basic concepts may be established for a dromotropic rate responsive algorithm.

Relationship between atrioventricular delay and oxygen consumption in patients with sick sinus syndrome: relevance to rate responsive pacing

To develop a dromotropic-controlled rate adaptive algorithm for patients with sick sinus syndrome (SSS) and intact AV conduction, 14 pace-maker patients with SSS underwent cardiopulmonary exercise testing (CPX). During exercise, the pace-maker was programmed in an AAT mode without rate adaptation, whereby 3 patients developed supraventricular arrhythmia and 11 patients kept sinus rhythm. Chronotropic incompetence (CI) at heart rate (HR) < 95 beats/min at the anaerobic threshold (AT) was found in five patients. In patients with chronotropic competence (CC), the HR increase was significantly greater than in CI patients (rest: 73.2 +/- 12.6 vs. 64.2 +/- 4.0 beats/min;AT:101.2 +/- 6.2 vs. 82.0 +/- 5.1 beats/min;peak: 135.2 +/- 10.7 vs. 103.2 +/- 10.9 beats/min). There was no significant difference in the AVD between CC and CI patients (rest: 167.7 +/- 38.6 vs. 170.8 +/- 22.5 ms, AT: 156.2 +/- 30.7 vs. 163.6 +/- 21.6 ms, peak: 144.7 +/- 29.0 vs. 152.4 +/- 15.0 ms). The correlation coefficient between HR increase and VO2 was +1.0 and between AVD decrease and VO2 - 1.0 in both groups. An increase in pacing rate from 75 beats/min to 120 beats/min without exercise (overpacing) led to a prolongation of the AV interval of about 30.6 +/- 14.2 ms. Based on this closed loop control with negative feedback, a dromotropic rate adaptive algorithm for patients with SSS and intact AV conduction could be developed.

Effect of different AV delays on left ventricular diastolic function and ANF levels in DDD paced hypertensive patients during daily activity and exercise

Fifteen hypertensive patients (13 men) with left ventricular hypertrophy, mean age 69 6 5 years, having complete heart block and paced in the DDD mode, were studied by two-dimensional and Doppler echo in 100 and 200 ms atrioventricular delays. ANF plasma levels were measured at rest and at peak exercise, during pacing with the two different atrioventricular delays. ANF plasma levels were significantly higher at pacing with long atrioventricular delays (200 ms), at rest (152.47 6 12.38 pg/mL vs 119 6 12.38 pg/mL, P, 0.001) and at exercise (180.93 6 11.51 vs 123.67 6 16.24 pg/mL, P, 0.0001). ANF plasma levels were significantly increased at exercise, compared to those at rest during pacing with the two different atrioventricular delays, but we found a more pronounced increase of ANF levels (from 152.47 6 10.49 pg/mL to 180.93 6 11.51 pg/mL), when the atrioventricular delays was set to 200 ms (P, 0.0001). A significant decrease of isovolumic relaxation time (from 123.33 6 20.5 to 105.33 6 11.06 ms, P, 0.001) was observed, during pacing with the short atrioventricular delays. Moreover, the peak early (E) to peak atrial (A) velocity ratio (E/A) was declined (from 0.89 6 0.7 to 0.57 6 0.18, P, 0.05). We also noticed that patients with small left ventricles exhibit greater increase in ANF plasma levels during DDD pacing with long atrioventricular delays (r 5 20.792, P 5 0.000). In conclusion, left ventricular diastolic function of our patients seems to be improved during DDD pacing with short (100 ms) atrioventricular delays, as it was expressed by echocardiographic and hormonal measurements.

Exercise prescription for patients with pacemakers

When developing an exercise program for pacemaker patients, basic information about the pacemaker must be understood. Atrial, ventricular, and dual-chamber devices can produce varying exercise responses and impact the exercise prescription. The type of rate adaptive sensor the pacemaker has will affect the nature of heart rate response, and therefore, must be taken into account when prescribing exercise. While rate modulation is used with most chronotropically incompetent patients, individuals with VVI pacemakers will also benefit from regular exercise. Although the value of exercise testing pacemaker-dependent patients for ECG interpretation may be limited, it is useful in determining exercise capacity and ensuring proper pacemaker function. Participation in a supervised exercise training program can greatly enhance the follow-up and management of pacemaker-dependent patients as well as afford them the opportunity to experience the physical and psychologic benefits typically associated with cardiac rehabilitation.

Atrial fibrillation is associated with a lower exercise capacity in male chronic heart failure patients

OBJECTIVE

To study the influence of atrial fibrillation on peak oxygen uptake (peak VO2) in chronic heart failure. An unfavourable effect of atrial fibrillation has been shown in several patient populations, but the results have not been consistent in chronic heart failure.

METHODS

Data were analysed from male heart transplant candidates who were able to perform graded bicycle ergometry until exhaustion with respiratory gas analysis and measurement of heart rate. Patients in atrial fibrillation (n = 18) were compared with patients in sinus rhythm (n = 93).

RESULTS

Age, weight, height, and aetiology of chronic heart failure did not differ significantly between the two groups. Cardiac catheterisation at supine rest showed that heart rate was comparable, but that stroke volume and cardiac output were lower (p < 0.05) in atrial fibrillation. Systolic and diastolic left ventricular function, assessed by radionuclide angiography at rest, were not significantly different. Peak VO2 (mean (SD): 13.8 (3.6) v 17.1 (5.6) ml/kg/min; p < 0.01) and peak work load (78 (27) v 98 (36) W; p < 0.05) were lower in the patients with atrial fibrillation, though respiratory gas exchange ratio and Borg score were similar in the two groups. Patients with atrial fibrillation had a higher heart rate sitting at rest before exercise (93 (16) v 84 (16) beats/min) and at peak effort (156 (23) v 140 (25) beats/min) (p < 0.05).

CONCLUSIONS

Atrial fibrillation is associated with a 20% lower peak VO2 in patients with chronic heart failure, suggesting that preserved atrial contraction or a regular rhythm, or both, are critical to maintain cardiac output and exercise performance.

A prospective multicenter study demonstrating clinical benefit with a new accelerometer-based DDDR pacemaker. Dromos Dr Investigators Group

From November 1994 to October 1995, 63 patients (average age 66 years; 41 men) from 15 centers implanted with the Biotronik Dromos DR and Ergos TC 03 pulse generators were prospectively screened with an exercise test in the DDD mode for the presence of chronotropic incompetence (CI). Both pulse generators incorporate an identical accelerometer-based motion sensor. CI was defined as a maximum heart rate < 60% of age predicted maximum heart rate or 100 beats/min. Twenty-five patients (40%) met the criteria for CI. Two weeks later, CI patients were required to complete paired metabolic exercise testing in the DDD and DDDR modes on consecutive days with a 24-hour rest period. The order of testing was randomized and performed double blinded to minimize potential biases. Three patients who did not reach the anaerobic threshold (AT) and one patient who was unable to perform the metabolic testing were excluded from the analysis. Compared to the DDD mode, there were statistically significant improvements in the DDDR mode for all five endpoints: heart rate (84 +/- 3.6 vs 113 +/- 3.5 beats/min; P < 0.0001); total exercise time (8.23 +/- 0.71 vs 9.15 +/- 0.65 min; P = 0.0005); maximum VO2 (17.76 +/- 1.36 vs 20.43 +/- 1.75 mL/kg per min; P = 0.0001); VO2 at AT (13.1 +/- 0.87 vs 14.59 +/- 0.79 mL/kg per min; P < 0.01); and exercise time to AT (5.65 +/- 0.61 vs 6.33 +/- 0.53 min; P = 0.02). In conclusion, the results of paired metabolic exercise tests with the Dromos DR and Ergos TC 03 pulse generators demonstrate a clear clinical benefit using the accelerometer-based sensor in the CI patient.